[Free Dsp] Unfinished Self Oscillating Filter
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A work in progress analog filter.
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Requires oversampling or the high frequencies will alias. You can hear this in the video when the cutoff goes really high.
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This node uses a lot of CPU (2%-13%) and has an inaccurate cutoff frequency.
I'm releasing it now because I probably won't give out the code when it's finished.
However I thought it may be fun for someone to mess with or expand upon.Although it's a flawed design, you can replace the nonlinearity with any distortion element. You can also tap out audio from any of the stages. Here we tap out of the final stage, but you may take audio from anywhere in the circuit matrix... So there are at least a few things to play with in the design.
Griffin_Growl_Stereo.h
#pragma once #include <JuceHeader.h> #include <cmath> #include <array> #include <algorithm> #ifndef M_PI #define M_PI 3.14159265358979323846 #endif #ifndef NOISE_FEEDBACK_VOLUME #define NOISE_FEEDBACK_VOLUME 0.008f #endif #ifndef INPUT_SIGNAL_THRESHOLD #define INPUT_SIGNAL_THRESHOLD 1e-6f #endif // Fast tanh approximation struct TanhHelper { static inline float tanh(float x) { float x2 = x * x; float sh = x * (1.f + x2 * (1.f / 6.f + x2 * (1.f / 120.f))); return sh / std::sqrt(1.f + sh * sh); } }; // Transistor nonlinearity lookup table for (2/M_PI)*atan(7.5*x) namespace transistorHelpers { inline float lookupAdvancedTransistorNonlinearity(float x) { static const int TABLE_SIZE = 4096; static const float maxInput = 2.0f; static const float invStep = (TABLE_SIZE - 1) / (2.0f * maxInput); static float lookupTable[TABLE_SIZE]; static bool tableInitialized = false; if (!tableInitialized) { const float step = 2.0f * maxInput / (TABLE_SIZE - 1); for (int i = 0; i < TABLE_SIZE; i++) { float xi = -maxInput + i * step; lookupTable[i] = (2.0f / M_PI) * std::atan(7.5f * xi); } tableInitialized = true; } float clampedX = std::clamp(x, -maxInput, maxInput); float index = (clampedX + maxInput) * invStep; int indexInt = static_cast<int>(index); float frac = index - indexInt; return lookupTable[indexInt] * (1.f - frac) + lookupTable[indexInt + 1] * frac; } inline float advancedTransistorNonlinearity(float x, float /*drive*/) { return lookupAdvancedTransistorNonlinearity(x); } } namespace project { using namespace juce; using namespace hise; using namespace scriptnode; // Stereo filter using Newton-Raphson iteration. // Caches the filter coefficient (cachedBaseG) and maintains separate states for left/right channels. class JunoFilterStereo { public: JunoFilterStereo() : cutoff(1000.f), resonance(1.f), drive(7.5f), sr(44100.0), errorThresh(0.000001f), cachedBaseG(std::tan(1000.f * M_PI / 44100.0)) { for (int i = 0; i < 4; ++i) { yL[i] = 0.f; yR[i] = 0.f; } sL[0] = sL[1] = sL[2] = sL[3] = 0.f; sR[0] = sR[1] = sR[2] = sR[3] = 0.f; } inline void setCutoff(float c) { if (cutoff != c) { cutoff = c; cachedBaseG = std::tan(cutoff * M_PI / sr); } } inline void setResonance(float r) { resonance = r; } inline void setDrive(float) { drive = 7.5f; } inline void prepare(double sr_) { sr = sr_; cachedBaseG = std::tan(cutoff * M_PI / sr); } inline void reset() { for (int i = 0; i < 4; ++i) { yL[i] = 0.f; yR[i] = 0.f; } sL[0] = sL[1] = sL[2] = sL[3] = 0.f; sR[0] = sR[1] = sR[2] = sR[3] = 0.f; } // Process one stereo sample; returns {left, right}. inline std::pair<float, float> processSample(float inL, float inR) { const float g = cachedBaseG; // Left channel const float noiseL = (NOISE_FEEDBACK_VOLUME > 0.f && std::abs(inL) > INPUT_SIGNAL_THRESHOLD) ? NOISE_FEEDBACK_VOLUME * (randGen.nextFloat() * 2.f - 1.f) : 0.f; for (int iter = 0; iter < 20; ++iter) { const float prev_yL3 = yL[3]; float nl0 = transistorHelpers::advancedTransistorNonlinearity(inL - yL[0] - resonance * yL[3] + noiseL, drive); float nl1 = transistorHelpers::advancedTransistorNonlinearity(yL[0] - yL[1], drive); float nl2 = transistorHelpers::advancedTransistorNonlinearity(yL[1] - yL[2], drive); float nl3 = transistorHelpers::advancedTransistorNonlinearity(yL[2] - yL[3], drive); float f0 = g * nl0 + sL[0] - yL[0]; float f1 = g * nl1 + sL[1] - yL[1]; float f2 = g * nl2 + sL[2] - yL[2]; float f3 = g * nl3 + sL[3] - yL[3]; float h0 = 1.f - nl0 * nl0; float h1 = 1.f - nl1 * nl1; float h2 = 1.f - nl2 * nl2; float h3 = 1.f - nl3 * nl3; float j00 = -g * h0 - 1.f; float j03 = -g * resonance * h0; float j10 = g * h1; float j11 = -g * h1 - 1.f; float j21 = g * h2; float j22 = -g * h2 - 1.f; float j32 = g * h3; float j33 = -g * h3 - 1.f; float den = j00 * j11 * j22 * j33 - j03 * j10 * j21 * j32; yL[0] += (f1 * j03 * j21 * j32 - f0 * j11 * j22 * j33 - f2 * j03 * j11 * j32 + f3 * j03 * j11 * j22) / den; yL[1] += (f0 * j10 * j22 * j33 - f1 * j00 * j22 * j33 + f2 * j03 * j10 * j32 - f3 * j03 * j10 * j22) / den; yL[2] += (f1 * j00 * j21 * j33 - f0 * j10 * j21 * j33 - f2 * j00 * j11 * j33 + f3 * j03 * j10 * j21) / den; yL[3] += (f0 * j10 * j21 * j32 - f1 * j00 * j21 * j32 + f2 * j00 * j11 * j32 - f3 * j00 * j11 * j22) / den; if (std::abs(yL[3] - prev_yL3) <= errorThresh) break; } sL[0] = 2.f * yL[0] - sL[0]; sL[1] = 2.f * yL[1] - sL[1]; sL[2] = 2.f * yL[2] - sL[2]; sL[3] = 2.f * yL[3] - sL[3]; // Right channel const float noiseR = (NOISE_FEEDBACK_VOLUME > 0.f && std::abs(inR) > INPUT_SIGNAL_THRESHOLD) ? NOISE_FEEDBACK_VOLUME * (randGen.nextFloat() * 2.f - 1.f) : 0.f; for (int iter = 0; iter < 20; ++iter) { const float prev_yR3 = yR[3]; float nl0 = transistorHelpers::advancedTransistorNonlinearity(inR - yR[0] - resonance * yR[3] + noiseR, drive); float nl1 = transistorHelpers::advancedTransistorNonlinearity(yR[0] - yR[1], drive); float nl2 = transistorHelpers::advancedTransistorNonlinearity(yR[1] - yR[2], drive); float nl3 = transistorHelpers::advancedTransistorNonlinearity(yR[2] - yR[3], drive); float f0 = g * nl0 + sR[0] - yR[0]; float f1 = g * nl1 + sR[1] - yR[1]; float f2 = g * nl2 + sR[2] - yR[2]; float f3 = g * nl3 + sR[3] - yR[3]; float h0 = 1.f - nl0 * nl0; float h1 = 1.f - nl1 * nl1; float h2 = 1.f - nl2 * nl2; float h3 = 1.f - nl3 * nl3; float j00 = -g * h0 - 1.f; float j03 = -g * resonance * h0; float j10 = g * h1; float j11 = -g * h1 - 1.f; float j21 = g * h2; float j22 = -g * h2 - 1.f; float j32 = g * h3; float j33 = -g * h3 - 1.f; float den = j00 * j11 * j22 * j33 - j03 * j10 * j21 * j32; yR[0] += (f1 * j03 * j21 * j32 - f0 * j11 * j22 * j33 - f2 * j03 * j11 * j32 + f3 * j03 * j11 * j22) / den; yR[1] += (f0 * j10 * j22 * j33 - f1 * j00 * j22 * j33 + f2 * j03 * j10 * j32 - f3 * j03 * j10 * j22) / den; yR[2] += (f1 * j00 * j21 * j33 - f0 * j10 * j21 * j33 - f2 * j00 * j11 * j33 + f3 * j03 * j10 * j21) / den; yR[3] += (f0 * j10 * j21 * j32 - f1 * j00 * j21 * j32 + f2 * j00 * j11 * j32 - f3 * j00 * j11 * j22) / den; if (std::abs(yR[3] - prev_yR3) <= errorThresh) break; } sR[0] = 2.f * yR[0] - sR[0]; sR[1] = 2.f * yR[1] - sR[1]; sR[2] = 2.f * yR[2] - sR[2]; sR[3] = 2.f * yR[3] - sR[3]; return { yL[3], yR[3] }; } private: double sr; float cutoff, resonance, drive, errorThresh; float cachedBaseG; float yL[4], sL[4]; float yR[4], sR[4]; juce::Random randGen; }; // Polyphonic stereo node. template <int NV> struct Griffin_Growl_Stereo : public data::base { SNEX_NODE(Griffin_Growl_Stereo); struct MetadataClass { SN_NODE_ID("Griffin_Growl_Stereo"); }; static constexpr bool isModNode() { return false; } static constexpr bool isPolyphonic() { return NV > 1; } static constexpr bool hasTail() { return false; } static constexpr bool isSuspendedOnSilence() { return false; } static constexpr int getFixChannelAmount() { return 2; } static constexpr int NumTables = 0, NumSliderPacks = 0, NumAudioFiles = 0, NumFilters = 0, NumDisplayBuffers = 0; float cutoffFrequency = 1000.f, resonance = 1.f; PolyData<JunoFilterStereo, NV> filters; inline void prepare(PrepareSpecs specs) { double sr = specs.sampleRate; filters.prepare(specs); for (auto& voice : filters) { voice.prepare(sr); voice.setDrive(7.5f); } } inline void reset() { for (auto& voice : filters) voice.reset(); } // Process block: scale inputs using fast tanh, process with filter, output stereo. template <typename ProcessDataType> inline void process(ProcessDataType& data) { auto& fixData = data.template as<ProcessData<getFixChannelAmount()>>(); auto audioBlock = fixData.toAudioBlock(); float* leftChannel = audioBlock.getChannelPointer(0); float* rightChannel = audioBlock.getChannelPointer(1); const int numSamples = static_cast<int>(data.getNumSamples()); const float tanhConst = TanhHelper::tanh(1.5f); for (int i = 0; i < numSamples; ++i) { float inL = TanhHelper::tanh(1.5f * leftChannel[i]) / tanhConst; float inR = TanhHelper::tanh(1.5f * rightChannel[i]) / tanhConst; float outL = 0.f, outR = 0.f; for (auto& voice : filters) { auto outs = voice.processSample(inL, inR); outL += outs.first; outR += outs.second; } outL /= NV; outR /= NV; leftChannel[i] = outL; rightChannel[i] = outR; } } template <typename FrameDataType> inline void processFrame(FrameDataType& data) {} // Parameter callback: update voices on change. template <int P> inline void setParameter(double v) { if (P == 0) { float newVal = static_cast<float>(v); if (cutoffFrequency != newVal) { cutoffFrequency = newVal; for (auto& voice : filters) voice.setCutoff(cutoffFrequency); } } else if (P == 1) { float newVal = static_cast<float>(v); if (resonance != newVal) { resonance = newVal; for (auto& voice : filters) voice.setResonance(resonance); } } } inline void createParameters(ParameterDataList& data) { parameter::data p1("Cutoff", { 20.0, 4000.0, 0.00001 }); registerCallback<0>(p1); p1.setDefaultValue(1000.0); data.add(std::move(p1)); parameter::data p2("Resonance", { 0.1, 4.3, 0.00001 }); registerCallback<1>(p2); p2.setDefaultValue(1.0); data.add(std::move(p2)); } inline void setExternalData(const ExternalData& ed, int index) {} inline void handleHiseEvent(HiseEvent& e) {} }; }Griffin_Growl_Mono.h
#pragma once #include <JuceHeader.h> #include <cmath> #include <array> #include <algorithm> #ifndef M_PI #define M_PI 3.14159265358979323846 #endif #ifndef NOISE_FEEDBACK_VOLUME #define NOISE_FEEDBACK_VOLUME 0.008f #endif #ifndef INPUT_SIGNAL_THRESHOLD #define INPUT_SIGNAL_THRESHOLD 1e-6f #endif // Fast tanh approximation struct TanhHelper { static inline float tanh(float x) { float x2 = x * x; float sh = x * (1.f + x2 * (1.f / 6.f + x2 * (1.f / 120.f))); return sh / std::sqrt(1.f + sh * sh); } }; // Transistor nonlinearity lookup table for (2/M_PI)*atan(7.5*x) namespace transistorHelpers { inline float lookupAdvancedTransistorNonlinearity(float x) { static const int TABLE_SIZE = 4096; static const float maxInput = 2.0f; static const float invStep = (TABLE_SIZE - 1) / (2.0f * maxInput); static float lookupTable[TABLE_SIZE]; static bool tableInitialized = false; if (!tableInitialized) { const float step = 2.0f * maxInput / (TABLE_SIZE - 1); for (int i = 0; i < TABLE_SIZE; i++) { float xi = -maxInput + i * step; lookupTable[i] = (2.0f / M_PI) * std::atan(7.5f * xi); } tableInitialized = true; } float clampedX = std::clamp(x, -maxInput, maxInput); float index = (clampedX + maxInput) * invStep; int indexInt = static_cast<int>(index); float frac = index - indexInt; return lookupTable[indexInt] * (1.f - frac) + lookupTable[indexInt + 1] * frac; } inline float advancedTransistorNonlinearity(float x, float /*drive*/) { return lookupAdvancedTransistorNonlinearity(x); } } namespace project { using namespace juce; using namespace hise; using namespace scriptnode; // Mono filter using Newton-Raphson iteration. // The filter coefficient is cached (cachedBaseG) and updated only when cutoff or sr change. class JunoFilterMono { public: JunoFilterMono() : cutoff(1000.f), resonance(1.f), drive(7.5f), sr(44100.0), errorThresh(0.000001f), cachedBaseG(std::tan(1000.f * M_PI / 44100.0)) { for (int i = 0; i < 4; ++i) y[i] = 0.f; s[0] = s[1] = s[2] = s[3] = 0.f; } inline void setCutoff(float c) { if (cutoff != c) { cutoff = c; cachedBaseG = std::tan(cutoff * M_PI / sr); } } inline void setResonance(float r) { resonance = r; } inline void setDrive(float) { drive = 7.5f; } inline void prepare(double sr_) { sr = sr_; cachedBaseG = std::tan(cutoff * M_PI / sr); } inline void reset() { for (int i = 0; i < 4; ++i) y[i] = 0.f; s[0] = s[1] = s[2] = s[3] = 0.f; } // Process one sample using cached filter coefficient. inline float processSample(float in) { // Use precomputed base coefficient (cachedBaseG) for all stages. const float g = cachedBaseG; // Generate noise only if input is nonzero. const float noise = (NOISE_FEEDBACK_VOLUME > 0.f && std::abs(in) > INPUT_SIGNAL_THRESHOLD) ? NOISE_FEEDBACK_VOLUME * (randGen.nextFloat() * 2.f - 1.f) : 0.f; // Newton-Raphson iteration (max 20 iterations) for (int iter = 0; iter < 20; ++iter) { const float prev_y3 = y[3]; const float nl0 = transistorHelpers::advancedTransistorNonlinearity(in - y[0] - resonance * y[3] + noise, drive); const float nl1 = transistorHelpers::advancedTransistorNonlinearity(y[0] - y[1], drive); const float nl2 = transistorHelpers::advancedTransistorNonlinearity(y[1] - y[2], drive); const float nl3 = transistorHelpers::advancedTransistorNonlinearity(y[2] - y[3], drive); const float f0 = g * nl0 + s[0] - y[0]; const float f1 = g * nl1 + s[1] - y[1]; const float f2 = g * nl2 + s[2] - y[2]; const float f3 = g * nl3 + s[3] - y[3]; const float h0 = 1.f - nl0 * nl0; const float h1 = 1.f - nl1 * nl1; const float h2 = 1.f - nl2 * nl2; const float h3 = 1.f - nl3 * nl3; const float j00 = -g * h0 - 1.f; const float j03 = -g * resonance * h0; const float j10 = g * h1; const float j11 = -g * h1 - 1.f; const float j21 = g * h2; const float j22 = -g * h2 - 1.f; const float j32 = g * h3; const float j33 = -g * h3 - 1.f; const float den = j00 * j11 * j22 * j33 - j03 * j10 * j21 * j32; y[0] += (f1 * j03 * j21 * j32 - f0 * j11 * j22 * j33 - f2 * j03 * j11 * j32 + f3 * j03 * j11 * j22) / den; y[1] += (f0 * j10 * j22 * j33 - f1 * j00 * j22 * j33 + f2 * j03 * j10 * j32 - f3 * j03 * j10 * j22) / den; y[2] += (f1 * j00 * j21 * j33 - f0 * j10 * j21 * j33 - f2 * j00 * j11 * j33 + f3 * j03 * j10 * j21) / den; y[3] += (f0 * j10 * j21 * j32 - f1 * j00 * j21 * j32 + f2 * j00 * j11 * j32 - f3 * j00 * j11 * j22) / den; if (std::abs(y[3] - prev_y3) <= errorThresh) break; } s[0] = 2.f * y[0] - s[0]; s[1] = 2.f * y[1] - s[1]; s[2] = 2.f * y[2] - s[2]; s[3] = 2.f * y[3] - s[3]; return y[3]; } private: double sr; float cutoff, resonance, drive, errorThresh; float cachedBaseG; float y[4], s[4]; juce::Random randGen; }; // Polyphonic mono node. template <int NV> struct Griffin_Growl_Mono : public data::base { SNEX_NODE(Griffin_Growl_Mono); struct MetadataClass { SN_NODE_ID("Griffin_Growl_Mono"); }; static constexpr bool isModNode() { return false; } static constexpr bool isPolyphonic() { return NV > 1; } static constexpr bool hasTail() { return false; } static constexpr bool isSuspendedOnSilence() { return false; } static constexpr int getFixChannelAmount() { return 2; } static constexpr int NumTables = 0, NumSliderPacks = 0, NumAudioFiles = 0, NumFilters = 0, NumDisplayBuffers = 0; float cutoffFrequency = 1000.f, resonance = 1.f; PolyData<JunoFilterMono, NV> filters; // Prepare voices; update sample rate only. inline void prepare(PrepareSpecs specs) { double sr = specs.sampleRate; filters.prepare(specs); for (auto& voice : filters) { voice.prepare(sr); voice.setDrive(7.5f); } } inline void reset() { for (auto& voice : filters) voice.reset(); } // Process audio block: apply fast tanh scaling, sum voices, process with filter, copy mono output to both channels. template <typename ProcessDataType> inline void process(ProcessDataType& data) { auto& fixData = data.template as<ProcessData<getFixChannelAmount()>>(); auto audioBlock = fixData.toAudioBlock(); float* leftChannel = audioBlock.getChannelPointer(0); float* rightChannel = audioBlock.getChannelPointer(1); const int numSamples = static_cast<int>(data.getNumSamples()); const float tanhConst = TanhHelper::tanh(1.5f); for (int i = 0; i < numSamples; ++i) { float in = TanhHelper::tanh(1.5f * leftChannel[i]) / tanhConst; float out = 0.f; for (auto& voice : filters) out += voice.processSample(in); out /= NV; leftChannel[i] = out; rightChannel[i] = out; } } template <typename FrameDataType> inline void processFrame(FrameDataType& data) {} // Parameter callback: update voices on change. template <int P> inline void setParameter(double v) { if (P == 0) { float newVal = static_cast<float>(v); if (cutoffFrequency != newVal) { cutoffFrequency = newVal; for (auto& voice : filters) voice.setCutoff(cutoffFrequency); } } else if (P == 1) { float newVal = static_cast<float>(v); if (resonance != newVal) { resonance = newVal; for (auto& voice : filters) voice.setResonance(resonance); } } } inline void createParameters(ParameterDataList& data) { parameter::data p1("Cutoff", { 20.0, 4000.0, 0.00001 }); registerCallback<0>(p1); p1.setDefaultValue(1000.0); data.add(std::move(p1)); parameter::data p2("Resonance", { 0.1, 4.3, 0.00001 }); registerCallback<1>(p2); p2.setDefaultValue(0.8); data.add(std::move(p2)); } inline void setExternalData(const ExternalData& ed, int index) {} inline void handleHiseEvent(HiseEvent& e) {} }; } -
